Revert to using matches insted of find with remote_download_regex

Reverts a change made in e8278ed alongside enabling `allowMultiple` for `--experimental_remote_download_regex`.

It is much easier to accidentally write regexes with pathological performance with `find` than with `matches`. If needed, the `find` functionality can always be obtained with `matches` by prepending and appending `.*` as needed.

In addition, common usage scenarios such as matching by file extension are easier to get right: With `matches`, `jar` will visibly fail to have an effect and is easily corrected to `.*jar` (or even `.*\.jar`), whereas with `find` it will silently fetch entire directories that contain the substring `jar`, potentially causing performance regressions.

Closes #16476.

PiperOrigin-RevId: 481186900
Change-Id: Iaa92c04c42bd4aebc33e7dc268225ab7722cd405

src/main/java/com/google/devtools/build/lib/remote/RemoteExecutionService.java

@@ -234,7 +234,7 @@ public RemoteExecutionService(
     this.shouldForceDownloadPredicate =
         path -> {
           for (Pattern pattern : patterns) {
-            if (pattern.matcher(path).find()) {
+            if (pattern.matcher(path).matches()) {
               return true;
             }
           }